1. Field of the Invention
The present invention relates to a vitreous silica crucible which is used for pulling single-crystal silicon, and more particularly, a vitreous silica crucible which is suitable for repeatedly pulling several times (multi-pulling) and is capable of suppressing erosion of the inner surface of the crucible at the time of pulling such that brown rings and the like are unlikely to be peeled from the inner surface of the crucible.
Priority is claimed on Japanese Patent Application No. 2007-339345, filed Dec. 28, 2007, the content of which is incorporated herein by reference.
2. Description of the Related Art
The pulling of single-crystal silicon is generally performed by the Czochralski method (CZ method) for pulling single-crystal silicon from a silicon melt fed into a vitreous silica crucible. In a process of pulling single-crystal silicon by the CZ method, as shown in FIG. 5, in an upper end of a portion in which a liquid level D of a silicon melt B in the vitreous silica crucible A is in contact with the inner surface of the crucible, an upper edge E of the liquid level D is in contact with the inner surface of the crucible in a state of slightly rising along the inner surface of the crucible A due to the surface tension of the silicon melt B. The rising portion of the liquid level D of the silicon melt is a three-phase interface portion E (meniscus portion) in which the glass surface of the crucible A, the silicon melt B and atmosphere gas C are adjacent to one another.
Generally, the inner surface of the crucible A which is in contact with the silicon melt B is eroded by reaction with the silicon melt B such that SiO is generated. Since the silicon melt B is thin in the three-phase interface portion E, the generated SiO is susceptible to be discharged to the atmosphere gas C. Accordingly, the three-phase interface portion E is eroded faster than that of the portion in which the inner surface of the crucible and the silicon melt B are in contact with each other at the lower portion of the liquid level D.
Since the inner surface of the crucible is susceptible to be eroded in the three-phase interface portion E, the concentration of the oxygen in a solution in the three-phase interface portion E becomes higher than other portions. Accordingly, if the volume of the three-phase interface portion E is large, the amount of oxygen introduced into the silicon melt is increased. Accordingly, the present applicant suggests a vitreous silica crucible capable of suppressing the amount of oxygen introduced into a silicon melt by increasing a contact angle between the liquid level of the silicon melt and the inner surface of a crucible and decreasing the volume of a three-phase interface portion (JP-A No. 2005-67910).
However, recently, in order to improve pulling efficiency of single-crystal silicon, a multi-pulling method of pulling the single-crystal silicon using a crucible a plurality of times is performed. In this method, a silicon melt is repeatedly charged in the crucible and the single-crystal silicon is pulled a plurality of times. In this pulling method, since the level of the silicon melt is vertically moved on the inner surface of the crucible according to the number of times of pulling and the three-phase interface portion is repeatedly moved on the inner surface of the crucible, the erosion amount of the inner surface of the crucible is increased although the total pulling amount is the same, compared with a method of pulling a long single-crystal silicon using one crucible.
Since the pulling is performed at a high temperature, brown rings (ring-shaped crystallization portions) which occur due to the reaction of vitreous silica and silicon or spots which occur due to the crystallization of the vitreous silica exist on the inner surface of the crucible at the time of pulling. If the three-phase interface portion of the liquid level of the silicon melt passes through the portion in which the brown rings or the crystal spots exist, the brown rings or the crystal spots are susceptible to be peeled from the inner surface of the crucible by the erosion of the inner surface of the crucible. If the brown rings or the crystal spots are peeled and mixed into the silicon melt, the yield of the single crystallization deteriorates.
The present invention provides a vitreous silica crucible and a vitreous silica crucible suitable for multi-pulling, in which brown rings or crystal spots are unlikely to be peeled from the inner surface of the crucible although a three-phase interface portion of a liquid level of a silicon melt is repeatedly moved along the inner surface of the crucible.